Fungal Spores

Abstract

Many heterotrophic eukaryotic organisms belong to the monophyletic kingdom Fungi. Because of their stationary life style, fungi reproduce by forming spores, cells that are specialised for dispersal to new locations by air, water or animals. Flagellated zoospores are produced by simple aquatic fungi. Most fungi are terrestrial, growing as hyphae and producing thick‐walled nonmotile spores. Asexual spores include sporangiospores and conidia, whereas sexual spores include zygospores, ascospores and basidiospores. Ascospores and basidiospores often are forcibly ejected into the air. Sporulation requires favourable nutritional and environmental conditions such as light and temperature, and involves cellular signalling and metabolic responses. As spores mature, their walls thicken, energy reserves such as lipid are acccumulated, and their metabolism decreases as they prepare for dormancy. Mature spores may undergo either exogenous or constitutive dormancy before germination. Upon germination, metabolic acitivity increases and a germ tube emerges from the spore.

Key Concepts:

  • Fungal spores have a unique role in fungal life cycles as they provide the genetic link between one generation and another.

  • Spores can be part of asexual or sexual reproductive cycles, and are sometimes borne by multicellular sporocarps.

  • Spores in part owe their success to their thick walls, reserve energy source, low metabolic rate and ability to withstand environmental stress that enables them to survive during dispersal.

  • Some fungi coevolved with insects, establishing mutualistic symbiotic relationships, and depend upon them for spore dispersal.

  • Sporulation occurs within a narrow range of special nutritional and environmental conditions, and involves signal transduction, gene activation and metabolic turnover.

  • Sporulation and spore germination of some fungi are coordinated with light and temperature changes marking day and night cycles, the seasons or with life cycles of their hosts.

  • Conditions required for germination reflect the particular biological adaptations and requirements of the fungus, and ensure that further somatic growth will be successful.

  • Scientists should understand spore biology so that they may better control animal, plant and human diseases; to better utilise fungi for industrial purposes, or to utilise them more effectively in the laboratory.

Keywords: fungal reproduction; spore discharge; spore distribution; spore physiology; life cycles (fungi)

Figure 1.

Light micrograph (inset: Bar, 5 μm) and electronmicrograph (Bar, 2 μm) of a spore (conidium) of Colletotrichum graminicola. The spore is surrounded by extracellular mucilage that lies outside the light‐coloured wall. The spore contains a single nucleus, vacuoles with electron‐dense contents and the electron‐transparent remains of extracted lipid bodies. From Mims CW, Richardson EA, Clay RP and Nicholson RL (1995) International Journal of Plant Science156: 9–18. © 1995 University of Chicago Press.

Figure 2.

A generalised fungal life cycle with both asexual and sexual reproduction. Within the sexual cycle, plasmogamy (P), karyogamy (K) and meiosis (M) occur. The thin red and blue lines each represent a haploid nuclear type, whereas the thick purple line represents a diploid nuclear type.

Figure 3.

An ascus containing nearly mature ascospores and the surrounding epiplasm. ×5400. Reproduced with permission from Mims CW, Richardson EA and Kimbrough JW (1990) Protoplasma156: 94–102. © 1990 Springer–Verlag.

Figure 4.

A cloud of ascospores discharged from cupulate sporocarps. Courtesy Plant Pathology Department, Cornell University, Ithaca, New York.

Figure 5.

Scanning elecronmicrograph of basidia and basidiospores. A single basidium in the foreground bears three basidiospores upon the elongate sterigmata. ×7600. Courtesy Yoon KS and McLaughlin DJ.

Figure 6.

This sporocarp of Ramaria sp. bears basidia and basidiospores as a thin layer covering the upright branches. After their ejection, the basidiospores can be carried away by air currents. (Photograph by Taylor F Lockwood.)

Figure 7.

Asexual spore types. (a) Chlamydospore formed within a hypha. (b) Sac‐like sporangium containing sporangiospores. Sporangiospores are released when the sporangial wall ruptures. (c) Zoosporangium producing zoospores internally. The zoospores escape through an opening and swim away. (d) Conidiophore bearing exogenous conidia that are easily dislodged when mature.

Figure 8.

Scanning electronmicrograph of Blumaria conidia that are germinating on the surface of their host plant. Each conidium can form more than one germ tube. (Electronmicrograph by Keith E Duncan. Reproduced by permission of DuPont Agricultural Biotechnology).

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Moore‐Landecker, Elizabeth(Aug 2011) Fungal Spores. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0000378.pub2]